Throughout high school and college I tutored tons of kids in math, ranging from elementary level to calculus and beyond, and while at first I believed that everyone might be able to achieve the results they wanted, after actually trying to help tons of students I realized that some of them would just never get it.

The attention to detail and rigor necessary for a lot of math is something that so many students were just entirely incapable of. I had some students, adults, who, no matter how many times they were told the same fact ("exponents don't distribute over addition", "dividing by zero is undefined"), would never remember it and make the same mistake every time I saw them.

Also, there's just a rampant unwillingness to even attempt to understand anything. So many students just wanted to memorize formulas, and would never develop an understanding of why any of the formulas worked or the process of how such formulas were discovered. I would tell them that they were digging themselves in a hole and that it would make it harder in the long run, but they were just so disinterested they didn't care. Math is hard, and it takes a certain degree of interest in it to overcome its difficulties and I doubt everyone is capable of obtaining sufficient interest.

And I think lying about how everyone is capable of math hurts a lot of students and wastes their time. In some cases we should just recognize that a student isn't going to make any progress and steer them to where they can use the talents they do have. It's pointless to have someone go over the same thing they'll never understand over and over again until they can muster a D-, just to forget it as soon as they're done. A complete waste of time.